1. Field of the Invention
The present invention relates to a fuel injection controller used for engines of ordinary automobiles, such as an inter-cylinder-injection fuel controller for controlling the torque produced by an engine by directly injecting the fuel into the cylinders. Particularly, the invention relates to an inter-cylinder-injection fuel controller for an internal combustion engine, which improves combustion and maintains operability without driving up the cost by correcting control parameters by clipping the air-to-fuel ratio to a lower-limit value, in order to suppress fluctuation in the engine running speed when an external load is exerted.
2. Prior Art
In internal combustion engines used for automobiles, in general, the fuel injectors are installed in an intake manifold of an intake pipe, so that the fuel is supplied into the cylinders together with the intaken air.
FIG. 7 is a diagram illustrating the constitution of a conventional fuel controller for an internal combustion engine having injectors provided in the intake pipe.
In FIG. 7, an internal combustion engine 1 is constituted by a plurality of cylinders. Here, only one cylinder is shown for simplicity.
An intake pipe 1a and an exhaust pipe 1b are communicated with a combustion chamber of the engine 1, and a crank shaft 1c is coupled to an end of the engine 1.
The intake pipe 1a supplies the intaken air and fuel to the engine 1, and the exhaust pipe 1b exhausts exhaust gases after burned in the engine 1. The crank shaft 1c rotates being linked to the engine 1. The cooling water 1d surrounding the periphery of the engine 1 cools the engine 1.
An air flow sensor 2 provided in an inlet port of the intake pipe 1a measures the amount of the air intaken by the engine 1 as amount-of-intaken-air data Qa.
A throttle valve 3 provided in the intake pipe 1a is opened and closed being interlocked to an accelerator pedal (not shown) operated by a driver, to adjust the amount Qa of the air intaken by the engine 1.
A throttle opening sensor 4 provided for the throttle valve 3 detects a position of the throttle valve 3, i.e., detects a throttle opening degree .theta..
A crank angle sensor 5 provided in relation to the crank shaft 1c outputs a pulse signal or a crank angle signal SGT in synchronism with the revolution of the crank shaft 1c. The crank angle signal SGT represents the running speed data of the engine 1 and the angular position data of the crank shaft 1c.
A water temperature sensor 6 for detecting the temperature Tw of the cooling water 1d works as a means for detecting the warmed-up state of the engine 1.
An oxygen sensor 7 provided in the exhaust pipe 1b detects the oxygen concentration Do in the exhaust gases exhausted from the engine 1 into the exhaust pipe 1b.
A control circuit 8 constituted by a microcomputer receives data (Qa, .theta., SGT, Tw, Do, etc.) detected by various sensors mounted on various peripheral portions of the engine, outputs drive control signals to various actuators (spark plugs and injectors that will be described later) depending upon the operation conditions, and executes a variety of sequence drive control operations (ignition timing control operation and fuel injection control operation) for each of the cylinders of the engine 1. Thus, the engine 1 is driven by combustion at desired ignition timings and at a desired air-to-fuel ratio.
A spark plug 9 provided in the combustion chamber in the cylinder of the engine 1 is driven by a spark control signal P from the control circuit 8.
A by-pass passage BP is so provided for the intake pipe 1a as to by-pass the throttle valve 3.
An air by-pass valve 10 provided in the by-pass passage BP is driven by a by-pass control signal B from the control circuit 8, opens and closes the by-pass passage BP so as to adjust the amount of the air by-passing the throttle valve 3, thereby to control the torque while the vehicle is running and to control the running speed of the engine during the idling operation (when the throttle valve 3 is fully closed).
An injector 11 is mounted in the intake manifold at a position on-the downstream side of the intake pipe 1a, and is driven by an injection control signal J from the control circuit 8 to supply fuel into the engine 1.
An EGR (exhaust gas reflux) pipe EP communicating the intake pipe 1a with the exhaust pipe 1b sends the exhaust gases exhausted from the engine back again to the combustion chamber so as to burn the exhaust gases again in order to decrease harmful NOx.
An EGR valve 12 provided in the EGR pipe EP is driven by an EGR control signal E from the control circuit 8 to control the amount of the exhaust gases refluxed into the intake pipe 1a from the exhaust pipe 1b.
A cylinder identifying sensor 13 attached to the cam shaft of the engine 1 sends, to the control circuit 8, a cylinder identifying signal SGC for identifying the cylinder in which the combustion is taking place in synchronism with the operation of the intake valve of the engine 1.
Detection signals Qa, .theta., SGT, Tw, Do and SGC obtained from the sensors 2, 4 to 7 and 13 are input to the control circuit 8. Actuators 9 to 12 are driven by control signals P, B, J and E output from the control circuit 8.
In a conventional device constituted as shown in FIG. 7, when an injection control signal J is output from the control circuit 8, the injector 11 is driven depending upon the drive pulse width of the injection control signal J, and the fuel of an amount corresponding to the injection control signal J is injected into the intake pipe 1a.
When the fuel is injected on the outside of the cylinder, however, the fuel partly adheres onto the inner walls of the intake pipe 1a and onto the intake valves of the engine before it is intaken into the cylinder of the engine 1. The fuel adheres particularly when the temperature is low (at the start of the operation) in which the fuel is less vaporized or during a transient operation condition where a response for the amount of fuel is required, resulting in the emission of exhaust gases containing harmful components in large amounts.
Therefore, there has heretofore been proposed an inter-cylinder-injection fuel controller for directly injecting fuel into the cylinders of the engine.
The inter-cylinder-injection fuel controller is drawing attention as an ideal engine, and offers the following effects (1) to (4) when it is used for a gasoline engine for general automobiles.
(1) Reducing the amount of toxic gases in the exhaust gases. PA1 (2) Improving the fuel efficiency. PA1 (3) Increasing the output of the engine 1. PA1 (4) Improving the controllability. PA1 An inter-cylinder-injection fuel controller for an internal combustion engine according to the present invention comprises: PA1 various sensors for outputting data representing operation conditions of the internal combustion engine; PA1 injectors for directly injecting the fuel into the cylinders of the internal combustion engine; and PA1 a control unit for operating the amounts of fuel supplied into the cylinders based upon the operation conditions and for controlling the injectors in a mode of the compression stroke injection or in a mode of the intake stroke injection based upon the amounts of supplying fuel; wherein PA1 said various sensors include an amount-of-intaken-air sensor for outputting data that corresponds to the amount of the air intaken by the internal combustion engine, and a crank angle sensor for outputting data that correspond to the running speed of the internal combustion engine and to the crank angle; and PA1 said control unit includes:
The fuel is directly injected near the spark plug 9 (see FIG. 7) in the combustion chamber. Therefore, the air-to-fuel ratio can be decreased (lean burn) without the need of taking a delay in the transportation of fuel into consideration, making it possible to reduce the amounts of toxic HC gas and CO gas.
The fuel is injected depending upon the ignition timing just before the ignition. Therefore, an inflammable fuel is formed around the spark plug 9 at the time of ignition, and the distribution of the mixture gas containing fuel becomes nonuniform, making it possible to establish a stratified combustion. This makes it possible to greatly decrease the apparent air-to-fuel ratio (to make the air-to-fuel ratio lean) of the amount of the supplied fuel to the amount of the air intaken into the cylinder of the engine 1.
Owing to the stratified combustion, furthermore, the EGR (exhaust gas reflux) that is effected in large amounts does not so much adversely affect the combustion, making it possible to increase the amount Qa of the intaken air. Therefore, the pumping loss decreases and the fuel efficiency is improved.
The mixture air concentrates around the ignition plug 9 and, hence, the end gas (mixture gas in a region remote from the spark plug 9) which causes knocking decreases. Owing to the stratified combustion, therefore, knocking occurs less, and the compression ratio of the engine 1 can be heightened.
Furthermore, the fuel vaporizes in the cylinder, and the vaporized fuel robs the air in the cylinder of the heat of vaporization. Therefore, the density of the intaken air increases, the volume efficiency increases, and the engine 1 produces an increased output.
Since the fuel is directly injected into the cylinder, the time delay is shortened from when the fuel is supplied until when the engine 1 produces an output by burning the fuel compared with the case of the device of FIG. 7. This makes it possible to realize an engine that quickly responds to the request of a driver.
In the inter-cylinder-injection fuel controller, there exist a lean operation mode in which the fuel is supplied in a very small amount during the compression stroke to establish a very lean stratified combustion to improve emission and fuel efficiency, and a stoichiometric operation mode in which the fuel is supplied in a required amount during the intake stroke to produce an increased output relying upon the combustion of an ordinary homogeneous mixture gas.
In the mode of the compression stroke injection (lean operation), the operation is carried out on the lean side compared with the mode of the intake stroke injection (stoichiometric operation). Therefore, the air Qa must be supplied in an increased amount to the engine 1 relative to a given throttle opening degree .theta. (accelerator opening degree). Therefore, the amount Qa of the intaken air that is usually controlled by the acceleration work only by the driver must be increased by another system.
FIG. 8 is a diagram illustrating the constitution of a conventional inter-cylinder-injection fuel controller of an internal combustion engine disclosed in, for example, Japanese Patent Laid-Open (Kokai) No. 187819/1992, and wherein the same constituent elements as those mentioned above are denoted by the same reference numerals but their description is not repeated.
This publication introduces a countermeasure on the side of the body of the engine 1 in order to improve combustion.
In FIG. 8, the control circuit 8A operates, for example, the amount of supplying fuel and the injection timing, outputs an injection control signal J depending upon the operated result, drives the injector 11A during at least either the intake stroke or the compression stroke, thereby to inject the fuel. Here, a cylinder to be controlled is identified based on a cylinder identifying signal SGC, to control the injector 11A of each of the cylinders.
The injector 11A is not mounted in the intake pipe 1a but is directly mounted in the combustion chamber of a cylinder of the engine 1, and has been designed to operate at high speeds and under high pressures, in order to inject a high-pressure fuel within a short period of time during the intake stroke or the compression stroke.
An injector driver 14 inserted between the control circuit 8A and the injector 11A converts the injection control signal J from the control circuit 8A into an injection control signal K for high-speed and high-pressure operation to thereby drive the injector 11A.
In response to the injection control signal J from the control circuit 8A, the injector driver 14 outputs an injection control signal K of an amplified large electric power to inject the fuel with a pressure overcoming the pressure in the cylinder.
The air by-pass valve 10A works to control the torque during the lean operation inclusive of when the vehicle is running in addition to controlling the running speed of the engine during the idling condition in which the throttle valve 3 is fully closed, and has been so designed as to increase the range for controlling the amount of the intaken air through the by-pass passage.
Described below is the operation of the conventional inter-cylinder-injection fuel controller for an internal combustion engine shown in FIG. 8.
In the inter-cylinder-injection device as described above, a stratified combustion (ultra-lean mode) control operation is carried out to supply fuel into the cylinder (compression stroke injection) just before the ignition, and the air-to-fuel ratio A/F has been controlled to be not smaller than 30 which is on the ultra-lean side. However, the air-to-fuel ratio in the practical combustion portion is close to a stoichiometric air-to-fuel ratio (14.7).
Unlike the lean combustion (intake stroke injection mode in which the intaken air and the fuel are homogeneously mixed together and, then, the mixture gas is burned at an air-to-fuel ratio of about 20) in the conventional device shown in FIG. 7, therefore, the operation is carried out near the air-to-fuel ratio of 16 (at which NOx is emitted in large amounts). Therefore, the EGR is introduced in large amounts to suppress the emission of NOx.
In the inter-cylinder-injection fuel controller of FIG. 8 as described above, the stratified combustion that is realized based upon injecting the fuel and finely controlling the ignition timing, is combined with the introduction of EGR in large amounts that tends to deteriorate the combustion in the engine 1, in order to establish a lean combustion by the injection in the compression stroke.
In the operation mode in which a large engine output is required such as during the acceleration, on the other hand, a homogeneous-mixture combustion is executed like in the conventional engine of FIG. 7 based upon the stoichiometric (rich) combustion by the injection in the intake stroke.
When the operation condition changes from the state of injection in the compression stroke (ultra-lean combustion) to the state of injection in the intake stroke (rich operation), in general, not only the air-to-fuel ratio and the EGR amount are corrected but also the fuel injection timing and the ignition timing are corrected. In this case, furthermore, the air by-pass valve 10A is controlled to decrease the amount Qa of the intaken air in order to suppress a change in the torque (increase of output) caused by a change from the lean fuel to the rich fuel.
When the air-to-fuel ratio is instantaneously shifted into a rich value, furthermore, a shock is generated due to a change in the torque. To prevent this, in general, the air-to-fuel ratio is gradually lowered, by a transient control called tailing mode, down to an air-to-fuel ratio at which the combustion takes place in the mode of the compression stroke injection (lean), which is then changed into the mode of the intake stroke injection to make the air-to-fuel ratio more rich.
In shifting the operation mode (tailing mode) as described above, however, when an external load is exerted in a state where the air-to-fuel ratio is rendered to be rich to such an extent at which the combustion can take place, deterioration in the combustion must be avoided; i.e., it is not almost allowed to render the air-to-fuel ratio to become rich. Therefore, it becomes difficult to effect the correction against a change in the torque caused by the external load.
In the lean operation mode in which an ultra-lean stratified combustion is established by supplying the fuel in the compression stroke, on the other hand, there exists a correlation between the output of the engine 1 and the amount of supplying the fuel. Therefore, when the external load is exerted on the engine 1 and the engine running speed has dropped, a change in the running speed can be suppressed by rendering the air-to-fuel ratio A/F to be rich.
In the conventional engine, furthermore, it has been proposed to suppress a change in the running speed by correcting, for example, the ignition timing. In the compression stroke injection mode, however, a change in the ignition timing causes a change in the phase relative to the fuel injection timing resulting in a change in the state of combustion. That is, the correction is not possible relying upon the ignition timing and, hence, a change in the running speed is suppressed by correcting the fuel.
When the air-to-fuel ratio is rendered to be too rich in the mode of the compression stroke injection, however, the combustion loses stability. In order to suppress the change in the running speed caused by the external load, therefore, when the air-to-fuel ratio is rendered to be rich so as to plunge into a region of unstable combustion, then, the change in the running speed may further increase due to more unstable combustion.
In the conventional inter-cylinder-injection fuel controller for an internal combustion engine as described above, the air-to-fuel ratio is rendered to be rich to suppress a change in the running speed when the external load is exerted. Therefore, a change in the running speed is further promoted when the air-to-fuel ratio has plunged into a region of unstable combustion.